Interconnect structure and method of forming same

ABSTRACT

A method comprises depositing a first dielectric layer over a substrate, forming a first metal line and a second metal line in the first dielectric layer, wherein the first metal line and the second metal line are separated from each other by a width approximately equal to a width of the first metal line, applying an etching process to the first metal line and the second metal line to form a first trench and a second trench, depositing a liner layer over the first dielectric layer and forming a via over the first metal line, wherein a bottom of the via is in direct contact with a top surface of the first metal line and the bottom of the via is conformal to the first trench.

BACKGROUND

The semiconductor industry has experienced rapid growth due tocontinuous improvements in the integration density of a variety ofelectronic components (e.g., transistors, diodes, resistors, capacitors,etc.). For the most part, this improvement in integration density hascome from repeated reductions in minimum feature size, which allows morecomponents to be integrated into a given area. As the demand for evensmaller electronic devices has grown recently, there has grown a needfor low resistance structures such as interconnects to further improvethe thermal performance of electronic devices.

A semiconductor device may include a variety of semiconductor structuressuch as transistors, capacitors, resistors and the like formed in asubstrate. One or more conductive layers formed of a metal, metal alloyand the like are separated by dielectric layers. There may be a varietyof interconnect structures formed between the conductive layers tointerconnect the semiconductor structures, provide an electricalconnection between a metal layer and its adjacent metal layer. Vias areformed in the dielectric layers to provide an electrical connectionbetween adjacent metal lines. In sum, metal lines and vias interconnectthe semiconductor structures and provide a conductive channel betweenthe semiconductor structures and the external contacts of thesemiconductor device.

A metal line and its adjacent via may be formed by using a dualdamascene process. According to the fabrication process of a dualdamascene structure, a dual damascene opening comprising a via portionand a trench portion is formed within a dielectric layer. The dualdamascene opening may be formed by photolithography techniques known inthe art. Generally, photolithography involves depositing a photoresistmaterial and then irradiating (exposing) and developing in accordancewith a specified pattern to remove a portion of the photoresistmaterial. The remaining photoresist material protects the underlyingmaterial from subsequent processing steps, such as etching. The etchingprocess may be a wet or dry, anisotropic or isotropic, etch process.After the etching process, the remaining photoresist material may beremoved. It should also be noted that the damascene interconnect openingmay be formed by one or more alternative process steps (e.g., a viafirst or a trench first damascene process).

After the dual damascene opening is formed, a barrier layer and a seedlayer may be formed along the sidewalls and the bottom of the dualdamascene opening. The barrier layer may be formed by suitablefabrication techniques such as various physical vapor deposition (PVD)techniques and the like. The seed layer may be formed by using suitablefabrication techniques such as PVD, electroless plating and the like.

Furthermore, an electroplating process may be applied to the dualdamascene opening. As a result, the dual damascene opening is filledwith a conductive material. The conductive material may comprise copper,although other suitable materials such as aluminum, alloys, tungsten,silver, doped polysilicon, combinations thereof, and/or the like, mayalternatively be utilized.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a cross sectional view of an interconnect structureof a semiconductor device in accordance with various embodiments of thepresent disclosure;

FIG. 2 illustrates a cross sectional view of another interconnectstructure of a semiconductor device in accordance with variousembodiments of the present disclosure;

FIG. 3 illustrates a cross sectional view of a semiconductor devicehaving a plurality of metal lines in accordance with various embodimentsof the present disclosure;

FIG. 4 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 3 after a first etching process is applied to the metallines in accordance with various embodiments of the present disclosure;

FIG. 5 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 4 after a second etching process is applied to thesidewalls of the inverted trapezoidal trenches in accordance withvarious embodiments of the present disclosure;

FIG. 6 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 5 after a dielectric layer is formed on the sidewalls andthe bottoms of the trenches in accordance with various embodiments ofthe present disclosure;

FIG. 7 illustrates a cross sectional view of the semiconductor deviceafter a dielectric layer is formed over the liner layer and a via isformed in the dielectric layer in accordance with various embodiments ofthe present disclosure; and

FIG. 8 illustrates a zoomed-in cross-sectional view of the semiconductordevice shown in FIG. 7 in accordance with various embodiments of thepresent disclosure.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the variousembodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the present embodiments are discussed in detailbelow. It should be appreciated, however, that the present disclosureprovides many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative of specific ways to make and use the disclosure,and do not limit the scope of the disclosure.

The present disclosure will be described with respect to embodiments ina specific context, namely an interconnect structure including aplurality of metal lines and vias. The embodiments of the disclosure mayalso be applied, however, to a variety of semiconductor devices.Hereinafter, various embodiments will be explained in detail withreference to the accompanying drawings.

FIG. 1 illustrates a cross sectional view of an interconnect structureof a semiconductor device in accordance with various embodiments of thepresent disclosure. The semiconductor device 100 includes a substrate102. A first dielectric layer 104 is formed over the substrate 102. Afirst conductive structure 112 and a second conductive structure 114 areembedded in the first dielectric layer 104. In some embodiments, thefirst conductive structure 112 is a first metal line. The secondconductive structure 114 is a second metal line. Throughout thedescription, the first conductive structure 112 is alternativelyreferred to as the first metal line 112. The second conductive structure114 is alternatively referred to as the second metal line 114.

As shown in FIG. 1, the top surfaces of the first metal line 112 and thesecond metal line 114 are not level with the top surface 103 of thefirst dielectric layer 104. Instead, there may be two invertedtrapezoidal trenches formed over the top surfaces of the first metalline 112 and the second metal line 114 respectively. The detailedformation process and the advantages of these two inverted trapezoidaltrenches will be described below with respect to FIGS. 3-7.

FIG. 1 further illustrates a second dielectric layer 110 formed over thefirst dielectric layer 104 and the top surfaces of the first metal line112 and the second metal line 114. In some embodiments, the seconddielectric layer 110 may function as a liner layer. The detailedfabrication process of the second dielectric layer 110 will be describedbelow with respect to FIG. 6.

The semiconductor device 100 may further comprise a third dielectriclayer 106 and a third conductive structure 116. As shown in FIG. 1, thethird dielectric layer 106 is deposited over the second dielectric layer110 and the third conductive structure 116 is embedded in the thirddielectric layer 106. In some embodiments, the third conductivestructure 116 is a via. Throughout the description, the third conductivestructure 116 is alternatively referred to as the via 116.

As shown in FIG. 1, a bottom portion of the via 116 is in direct contactwith a top surface of the first metal line 112. More particularly, thebottom portion of the via 116 is conformal to the sidewall of theinverted trapezoidal trench, which is formed over the first metal line112.

One advantageous feature of having the inverted trapezoidal trenchesover the metal lines (e.g., first metal line 112) is that the invertedtrapezoidal trenches help to increase the spacing between two adjacentconductive structures (e.g., the via 116 and the second metal line 114).

In accordance with some embodiments, during fabrication processes of thesemiconductor device 100, overlay alignment shift defects may cause ashift of the via 116 from the centerline of the first metal line 112 tothe edge of the first metal line 112. Such a shift may reduce thespacing between two adjacent conductive structures (e.g., the via 116and the second metal line 114). The reduced spacing may further affectthe semiconductor device's characteristics such as a short circuitbetween two adjacent conductive structures, breakdown voltagedegradation and/or the like. The advantages of having the invertedtrapezoidal trenches will be described in detail with respect to FIG. 8.

FIG. 2 illustrates a cross sectional view of another interconnectstructure of a semiconductor device in accordance with variousembodiments of the present disclosure. The interconnect structure aswell as the overlay alignment shift of the semiconductor device 200 issimilar to that of the semiconductor device 100 shown in FIG. 1 exceptthat the first metal line 112 and the second metal line 114 are replacedby a first gate structure 210 and a second gate structure 220respectively.

The substrate 102 may comprise a variety of electrical circuits such asmetal oxide semiconductor (MOS) transistors and the associated contactplugs (not shown respectively). For simplicity, only the first gatestructure 210 and the second gate structure 220 are presented toillustrate the innovative aspects of various embodiments.

Furthermore, the first gate structure 210 and the second gate structure220 may be the same structure. For simplicity, only the structure of thefirst gate structure 210 will be described in detail below.

As shown in FIG. 2, the first gate structure 210 includes a gatedielectric layer 212 formed over the substrate 102, a gate electrode 214formed over the gate dielectric layer 212 and gate spacers 216.

The gate dielectric layer 212 may be a dielectric material such assilicon oxide, silicon oxynitride, silicon nitride, an oxide, anitrogen-containing oxide, a combination thereof and/or the like. Thegate dielectric layer 212 may have a relative permittivity value greaterthan about 4. Other examples of such materials include aluminum oxide,lanthanum oxide, hafnium oxide, zirconium oxide, hafnium oxynitride,combinations thereof and/or the like. In an embodiment in which the gatedielectric layer 212 comprises an oxide layer, the gate dielectric layer212 may be formed by a plasma enhanced chemical vapor deposition (PECVD)process using tetraethoxysilane (TEOS) and oxygen as a precursor. Inaccordance with some embodiments, the gate dielectric layer 212 may beof a thickness in a range from about 8 Angstroms to about 200 Angstroms.

The gate electrode 214 may comprise a conductive material, such as ametal (e.g., tantalum, titanium, molybdenum, tungsten, platinum,aluminum, hafnium, ruthenium), a metal silicide (e.g., titaniumsilicide, cobalt silicide, nickel silicide, tantalum silicide), a metalnitride (e.g., titanium nitride, tantalum nitride), dopedpoly-crystalline silicon, other conductive materials, combinationsthereof and/or the like.

In some embodiments in which the gate electrode 214 is poly-silicon, thegate electrode 214 may be formed by depositing doped or undopedpoly-silicon by low-pressure chemical vapor deposition (LPCVD) to athickness in the range of about 400 Angstroms to about 2,400 Angstroms.

The spacers 216 may be formed by blanket depositing one or more spacerlayers (not shown) over the gate electrode 214 and the substrate 102.The spacer layers 216 may comprise suitable dielectric materials such assilicon nitride (SiN), oxynitride, silicon carbide (SiC), siliconoxynitride (SiON), oxide, any combinations thereof and/or the like. Thespacer layers 216 may be formed by commonly used techniques such aschemical vapor deposition (CVD), PECVD, sputtering and/or the like.

FIGS. 3-8 illustrate intermediate steps of fabricating the interconnectstructure shown in FIG. 1 in accordance with various embodiments of thepresent disclosure. FIG. 3 illustrates a cross sectional view of asemiconductor device having a plurality of metal lines in accordancewith various embodiments of the present disclosure. As shown in FIG. 3,the semiconductor device 300 comprises a first dielectric layer 104formed over the substrate 102. A first metal line 112 and a second metalline 114 are embedded in the first dielectric layer 104. In someembodiments, the top surfaces of the first metal line 112 and the secondmetal line 114 are exposed outside the first dielectric layer 104 asshown in FIG. 3.

In some embodiments, the width of the metal lines (e.g., first metalline 112) is defined as W. The spacing between two adjacent metal lines(e.g., first metal line 112 and second metal line 114) is defined as D.In some embodiments, W is approximately equal to 20 nm. D isapproximately equal to 20 nm.

The substrate 102 may be formed of suitable semiconductor materials suchas silicon, germanium, diamond, or the like. Alternatively, compoundmaterials such as silicon germanium, silicon carbide, gallium arsenic,indium arsenide, indium phosphide, silicon germanium carbide, galliumarsenic phosphide, gallium indium phosphide, combinations of these, andthe like, with other crystal orientations, may also be used.

Additionally, the substrate 102 may comprise a silicon-on-insulator(SOI) substrate. Generally, an SOI substrate comprises a layer of asemiconductor material such as epitaxial silicon, germanium, silicongermanium, SOI, silicon germanium on insulator (SGOI), or combinationsthereof. The substrate 102 may be doped with a p-type dopant, such asboron, aluminum, gallium, or the like, although the substrate mayalternatively be doped with an n-type dopant, as is known in the art.

The first dielectric layer 104 may be formed of a low-K dielectricmaterial such as fluorosilicate glass (FSG) and/or the like. The firstdielectric layer 104 may function as an inter-metal dielectric layer.The first dielectric layer 104 may be formed by suitable depositiontechniques such as PECVD techniques, high-density plasma chemical vapordeposition (HDPCVD) and/or the like.

The first metal line 112 and the second metal line 114 may be madethrough any suitable formation process (e.g., lithography with etching,damascene, dual damascene, or the like) and may be formed using suitableconductive materials such as copper, aluminum, aluminum alloys, copperalloys, any combinations thereof and/or the like.

In accordance with some embodiments, the first metal line 112 and thesecond metal line 114 may be formed through a damascene process, wherebymasks are deposited onto the surface of the first dielectric layer 104,openings are etched into the surface, and conductive material (such astungsten or copper) is used to fill the openings.

It should be noted that the first metal line 112 and the second metalline 114 may comprise one or more layers of conductive material. Forexample, the first metal line 112 and the second metal line 114 mayinclude barrier layers, adhesive layers, multiple conductive layers, orthe like.

The first dielectric layer 104 and the metal lines embedded in the firstdielectric layer 104 may be collectively called a first metallizationlayer. While FIG. 3 shows the first metallization layer formed over thesubstrate 102, one skilled in the art will recognize that moreinter-metal dielectric layers (not shown) and the associated metal linesand plugs (not shown respectively) may be formed between the firstmetallization layer and the substrate 102 shown in FIG. 3. Inparticular, the layers between the metallization layer and the substrateshown in FIG. 3 may be formed by alternating layers of dielectric (e.g.,extremely low-k dielectric material) and conductive materials (e.g.,copper).

FIG. 4 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 3 after a first etching process is applied to the metallines in accordance with various embodiments of the present disclosure.A suitable etching process such as wet-etching or dry-etching may beapplied to the first metal line 112 and the second metal line 114. Thedetailed operations of either the dry etching process or the wet etchingprocess are well known, and hence are not discussed herein to avoidrepetition. In accordance with an embodiment, after an etching processis employed to remove an upper portion of the metal lines, two invertedtrapezoidal trenches 402 and 404 are formed as shown in FIG. 4

In some embodiments, the depth of the inverted trapezoidal trenches 402and 404 is defined as H1 as shown in FIG. 4. The height of the remainingportion of the metal lines 112 and 114 is defined as H2. The originalthickness of the metal lines 112 and 114 prior to the etching process isdefined as H3. In according to some embodiments, H1 may be approximatelyequal to 10 nm. H2 may be approximately equal to 45 nm. H3 may beapproximately equal to 55 nm.

In some embodiments, the ratio of H1 to H2 is in a range from about 0.2to about 1. The ratio of H1 to H3 is in a range from about 0.167 toabout 0.5. Moreover, the sidewall of the inverted trapezoidal trenches(e.g., the inverted trapezoidal trench 404) and the horizontal axis forman angle α as shown in FIG. 4. In some embodiments, a is approximatelyequal to 87 degrees.

FIG. 5 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 4 after a second etching process is applied to thesidewalls of the inverted trapezoidal trenches in accordance withvarious embodiments of the present disclosure. In some embodiments, thesecond etching process may be a dry-etching process. The detailedoperations of the dry etching process are well known, and hence are notdiscussed herein to avoid repetition. In accordance with someembodiments, the second etching process is employed to trim thesidewalls of the inverted trapezoidal trenches 402 and 404 so as todefine the corner facets of the trenches.

After the second etching process is applied to the sidewalls of theinverted trapezoidal trenches 402 and 404, portions of the sidewalls areremoved as a result. In some embodiments, as shown in FIG. 5, thesidewall of the inverted trapezoidal trench 404 and the horizontal axisform an angle β as shown in FIG. 5. In some embodiments, the angle β isgreater than or equal to 45 degrees.

FIG. 6 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 5 after a dielectric layer is formed on the sidewalls andthe bottoms of the trenches in accordance with various embodiments ofthe present disclosure. The second dielectric layer 110 is depositedover the first dielectric layer 110 as well as the inverted trapezoidaltrenches 402 and 404. As shown in FIG. 6, the second dielectric layer110 is conformal to the inverted trapezoidal trenches 402 and 404.

In some embodiments, the second dielectric layer 110 is a liner layer.The liner layer may be a high etch selectivity layer. In addition, theliner layer may function as an etch stop layer. Throughout thedescription, the second dielectric layer 110 is alternatively referredto as the liner layer 110. The liner layer 110 may be formed of anysuitable dielectric materials such as TEOS, silicon nitride, oxide,silicon oxynitride, low-K dielectric materials, high-K dielectricmaterials and/or the like.

The liner layer 110 may be formed using suitable fabrication processessuch as a PECVD process, although other suitable processes, such as PVD,atomic layer deposition (ALD) and/or the like, may alternatively beused. Additionally, the liner layer 110 may be formed to a thickness ina range from about 10 Angstroms to about 50 Angstroms.

FIG. 7 illustrates a cross sectional view of the semiconductor deviceafter a dielectric layer is formed over the liner layer and a via isformed in the dielectric layer in accordance with various embodiments ofthe present disclosure. The third dielectric layer 106 may be similar tothe first dielectric layer 104, and hence is not discussed in furtherdetail herein to avoid repetition.

In accordance with some embodiments, the third dielectric layer 106 maybe patterned using, e.g., a photolithographic masking and etchingprocess, whereby a photolithographic mask (not shown in FIG. 7) isformed over the third dielectric layer 106 and then exposed to apatterned light.

After exposure, desired portions of the photolithographic mask areremoved to expose the underlying dielectric layer 106, which may then beetched to remove the exposed portions, thereby patterning the thirddielectric layer 106 to form an opening (not shown). It should be notedthat the opening may be formed by any other suitable semiconductorpatterning techniques such as an etching process, a laser ablationprocess, any combinations thereof and/or the like.

A barrier layer (not shown) may be deposited on the surface of theopening. The barrier layer may be formed of titanium, titanium nitride,tantalum, tantalum nitride, and combinations thereof and/or the like.The barrier layer may be formed using suitable fabrication techniquessuch as ALD, PECVD, plasma enhanced physical vapor deposition (PEPVD)and/or the like.

A seed layer (not shown) may be formed over the barrier layer. The seedlayer may be may be formed of copper, nickel, gold, any combinationthereof and/or the like. The seed layer may be formed by any suitabledeposition techniques such as PVD, CVD and/or the like. The seed layermay have a thickness in a range from about 50 Angstroms to about 1,000Angstroms.

In addition, the seed layer may be alloyed with a material that improvesthe adhesive properties of the seed layer so that it can act as anadhesion layer. For example, the seed layer may be alloyed with amaterial such as manganese or aluminum, which will migrate to theinterface between the seed layer and the barrier layer and will enhancethe adhesion between these two layers. The alloying material may beintroduced during formation of the seed layer. The alloying material maycomprise no more than about 10% of the seed layer.

A conductive material may be filled in the opening to form a via 116coupled to the first metal line 112. In particular, the bottom of thevia 116 is in direct contact with the top surface of the first metalline 112.

During the fabrication process of the via 116, an overlay alignmentshift defect may occur and cause a shift of the via 116 from thecenterline of the first metal line 112 to the edge of the first metalline 112 as shown in FIG. 7. Although the via 116 is shifted to one sideof the first metal line 112, the bottom of the via 116 is conformal tothe sidewall of the inverted trapezoidal trench as shown in FIG. 7.

Such a via shown in FIG. 7 may be alternatively referred to as aself-aligned via because, after a less precise alignment such as analignment shift, the bottom of the via is aligned with the sidewall ofthe inverted trapezoidal trench. Such an alignment helps to improve thespacing between the via and the adjacent mental lines (e.g., the via 116and the second metal line 114). The detailed description of theimprovement will be illustrated below with respect to FIG. 8.

The conductive material filled in the opening may be copper, but can beany suitable conductive materials, such as copper alloys, aluminum,tungsten, silver, any combinations thereof and/or the like. Theconductive material may be formed by suitable techniques such as anelectro-less plating process, CVD, electroplating and/or the like.

A planarization process is performed to remove excess conductivematerials in accordance with various embodiments. The planarizationprocess may be implemented by using suitable techniques such asgrinding, polishing and/or chemical etching, a combination of etchingand grinding techniques.

In accordance with some embodiments, the planarization process may beimplemented by using a chemical mechanical polishing (CMP) process. Inthe CMP process, a combination of suitable etching materials andabrading materials are put into contact with the top surface of thesemiconductor device and a grinding pad (not shown) is used to grindaway excess copper.

FIG. 8 illustrates a zoomed-in cross-sectional view of the semiconductordevice shown in FIG. 7 in accordance with various embodiments of thepresent disclosure. As described above with respect to FIG. 7, somelevel of misalignment may occur due to a variety of overlay alignmentshift defects. The misalignment may reduce the spacing between the via116 and the second metal line 114. However, the inverted trapezoidaltrenches may help to increase the spacing between the via 116 and thesecond metal line 114.

As shown in FIG. 8, the actual spacing between the via 116 and thesecond metal line 114 is defined as L1. On the other hand, withouthaving an inverted trapezoidal trench over the first metal line 112, thespacing between the via 116 and the second metal line 114 is defined asL2 as shown in FIG. 8.

FIG. 8 shows L1 and L2 are sides of a right triangle. In particular, L1is a side opposite the right angle of a right triangle. L2 is a leg ofthe right triangle. As such, the value of L1 is greater than the valueof L2. Therefore, the spacing may be improved after an invertedtrapezoidal trench (e.g., the trench over the first metal line 112) isemployed as shown in FIG. 8.

In accordance with an embodiment, an apparatus comprises a firstdielectric layer formed over a substrate, a first conductive structureembedded in the first dielectric layer, wherein a top surface of thefirst conductive structure and a surface of the first dielectric layerform a first inverted trapezoidal shape, a second conductive structureembedded in the first dielectric layer, wherein a top surface of thesecond conductive structure and the surface of the first dielectriclayer form a second inverted trapezoidal shape, a second dielectriclayer formed over the first dielectric layer and a third conductivestructure embedded in the second dielectric layer, wherein a bottom ofthe third conductive structure is in direct contact with the top surfaceof the first conductive structure and the bottom of the third conductivestructure is conformal to the first inverted trapezoidal shape.

In accordance with an embodiment, a method comprises depositing a firstdielectric layer over a substrate, forming a first conductive structureand a second conductive structure in the first dielectric layer, whereina top surface of the first conductive structure and a top surface of thesecond conductive structure are exposed outside the first dielectriclayer, recessing the first conductive structure and the secondconductive structure to form a first trench and a second trench,depositing a liner layer over the first dielectric layer, depositing asecond dielectric layer over the liner layer and forming a thirdconductive structure in the second dielectric layer, wherein a bottom ofthe third conductive structure is in direct contact with the top surfaceof the first conductive structure and the bottom of the third conductivestructure is conformal to the first trench.

In accordance with an embodiment, a method comprises depositing a firstdielectric layer over a substrate, forming a first metal line and asecond metal line in the first dielectric layer, wherein the first metalline and the second metal line are separated from each other by a widthapproximately equal to a width of the first metal line, applying anetching process to the first metal line and the second metal line toform a first trench and a second trench, depositing a liner layer overthe first dielectric layer and forming a via over the first metal line,wherein a bottom of the via is in direct contact with a top surface ofthe first metal line and the bottom of the via is conformal to the firsttrench.

Although embodiments of the present disclosure and its advantages havebeen described in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the disclosure as defined by the appendedclaims.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the present disclosure, processes, machines,manufacture, compositions of matter, means, methods, or steps, presentlyexisting or later to be developed, that perform substantially the samefunction or achieve substantially the same result as the correspondingembodiments described herein may be utilized according to the presentdisclosure. Accordingly, the appended claims are intended to includewithin their scope such processes, machines, manufacture, compositionsof matter, means, methods, or steps.

What is claimed is:
 1. A method comprising: depositing a firstdielectric layer over a substrate; forming a first conductive structureand a second conductive structure in the first dielectric layer, whereina top surface of the first conductive structure and a top surface of thesecond conductive structure are exposed outside the first dielectriclayer; recessing the first conductive structure and the secondconductive structure to form a first trench and a second trench, whereina bottom portion of a sidewall of the first trench is formed of adielectric material; depositing a liner layer over the first dielectriclayer; depositing a second dielectric layer over the liner layer; andforming a third conductive structure in the second dielectric layer,wherein: a bottom of a first portion of the third conductive structureis a planar surface and is in direct contact with the top surface of thefirst conductive structure, and wherein a rightmost edge of the bottomof the first portion is vertically aligned with a rightmost edge of thefirst conductive structure; and a bottom of a second portion of thethird conductive structure is a slope surface and is in direct contactwith the first dielectric layer, and wherein a leftmost edge of thebottom of the second portion is vertically aligned with the rightmostedge of the first conductive structure.
 2. The method of claim 1,wherein: the first trench is of an inverted trapezoidal shape; and thesecond trench is of an inverted trapezoidal shape.
 3. The method ofclaim 2, wherein: the liner layer is a high etch selectivity layer; theliner layer is conformal to the inverted trapezoidal shape of the firsttrench and the second trench; and the liner layer is of a thickness in arange from about 10 Angstroms to about 50 Angstroms.
 4. The method ofclaim 1, further comprising: removing portions of the first dielectriclayer, wherein the portions are adjacent to the first trench and thesecond trench.
 5. The method of claim 4, further comprising: during thestep of removing portions of the first dielectric layer, applying a dryetching process to sidewalls of the first dielectric layer, wherein thesidewalls are adjacent to the first conductive structure and the secondconductive structure.
 6. The method of claim 1, further comprising:recessing the first conductive structure and the second conductivestructure until a ratio of a depth of the first trench to a thickness ofthe first conductive structure is in a range from about 0.2 to about 1.7. The method of claim 1, further comprising: recessing the firstconductive structure and the second conductive structure until a ratio adepth of the second trench to a thickness of the second conductivestructure is in a range from about 0.2 to about
 1. 8. A methodcomprising: depositing a first dielectric layer over a substrate;forming a first metal line and a second metal line in the firstdielectric layer, wherein the first metal line and the second metal lineare separated from each other by a width approximately equal to a widthof the first metal line, and wherein top surfaces of the first metalline and the second metal line are level with a top surface of the firstdielectric layer after forming the first metal line and the second metalline; applying an etching process to the first metal line and the secondmetal line to form a first trench and a second trench, wherein theentire top surface of the first metal line is lower than the top surfaceof the first dielectric layer after the step of applying the etchingprocess to the first metal line and the second metal line; depositing aliner layer over the first dielectric layer; and forming a via over thefirst metal line, wherein: a bottom of a first portion of the via is aflat surface and is in direct contact with a top surface of the firstmetal line; and a bottom of a second portion of the via is a slopesurface and is in direct contact with the first dielectric layer.
 9. Themethod of claim 8, wherein: the first trench is of an invertedtrapezoidal shape; and the second trench is of the inverted trapezoidalshape.
 10. The method of claim 8, wherein: the liner layer is of athickness in a range from about 10 Angstroms to about 50 Angstroms. 11.The method of claim 8, wherein: the step of depositing the liner layerover the first dielectric layer is performed by chemical vapordeposition (CVD) process.
 12. The method of claim 8, wherein: the stepof forming the first metal line and the second metal line in the firstdielectric layer is performed by a single damascene process.
 13. Themethod of claim 8, wherein: the step of forming the first metal line andthe second metal line in the first dielectric layer is performed by adual damascene process.
 14. A method comprising: depositing a firstdielectric layer on a substrate; forming a first conductive structure inthe first dielectric layer; recessing the first conductive structure toform a first trench over the first conductive structure, wherein thefirst trench has an inverted trapezoidal shape and a top surface of thefirst conductive structure extends from a first corner of the firsttrench to a second corner of the first trench after recessing the firstconductive structure; depositing a second dielectric layer over thefirst dielectric layer; and forming a third conductive structure in thesecond dielectric layer, wherein: a bottom of the third conductivestructure is within the first trench and the bottom of the thirdconductive structure includes a flat bottom and a sloped bottom, whereinthe flat bottom is in direct contact with a top surface of the firstconductive structure and the sloped bottom is in direct contact with thefirst dielectric layer, and wherein a rightmost edge of the flat bottomis vertically aligned with a rightmost edge of the first conductivestructure and a leftmost edge of the sloped bottom is vertically alignedwith the rightmost edge of the first conductive structure; and thebottom of the third conductive structure is conformal to the invertedtrapezoidal shape.
 15. The method of claim 14, wherein: a top surface ofthe first conductive structure and a surface of the first dielectriclayer form the inverted trapezoidal shape.
 16. The method of claim 14,further comprising: prior to the step of recessing the first conductivestructure to form the first trench over the first conductive structure,forming a second conductive structure in the first dielectric layer,wherein a top surface of the second conductive structure is level with atop surface of the first conductive structure; and recessing the secondconductive structure to form a second trench over the second conductivestructure.
 17. The method of claim 16, wherein: a top surface of thesecond conductive structure and a surface of the first dielectric layerform a second inverted trapezoidal shape.
 18. The method of claim 16,wherein: the first conductive structure is a first metal line of aninterconnect structure; and the second conductive structure is a secondmetal line of the interconnect structure.
 19. The method of claim 14,wherein: the third conductive structure is a via.
 20. The method ofclaim 14, further comprising: depositing a liner layer disposed betweenthe first dielectric layer and the second dielectric layer, wherein theliner layer is conformal to a surface of the first dielectric layer.